Liming Impacts on Soils, Crops, and Biodiversity in the UK

Introduction

Fertile soil is essential for food security, but soil degradation issues like acidification are worsened by poor management.
There's a global interest in sustainable soil management, including reassessing existing practices.
Liming, an established method for improving acidic soils, has well-understood short-term impacts on soil biota and nitrogen cycling but variable effects on carbon storage depending on soil type, land use, and climate.
Liming affects all soil elements, leading to changes in soil processes that influence plant nutrient uptake, increasing phosphorus availability and decreasing toxic heavy metal uptake.
Soil physical conditions are maintained or improved by liming and arable crops often show a positive yield response related to soil pH levels.
Liming influences crop disease development, requiring management adjustments based on crop type within rotations.
Repeated lime applications can improve grassland biomass production and mineral content, with implications for livestock systems.
Ecological studies show positive impacts on biodiversity, such as increased earthworm abundance, which benefits wading birds in upland grasslands.
A qualitative framework explores liming's impacts on soil and crop processes, considering functional aspects in ecosystem services and how these impacts change over time.

Key Factors Influencing Liming Management

Management of lime is complex due to differences in land use and varied management objectives.

Lime Material Type and Quality

Ground limestone ( $CaCO<em>3$ ) is the most common liming material, followed by dolomitic limestone ( $CaMg(CO</em>3)_2$ ).
Other materials include slaked lime ( $Ca(OH)_2$ ), pelletized materials, shell sands, and burnt lime ( $CaO$ ).
Industrial gypsum-like by-products, composts, and digestate materials also have liming value.
Quality characteristics of liming materials:
- Neutralizing Value (NV): The amount of acidity a material can neutralize, expressed relative to pure $CaO$ .
- Particle Size: Finer material is more effective for increasing soil pH and reducing exchangeable aluminum ( $Al$ ).
UK regulations require sellers to describe limestone products in terms of NV and the percentage passing through a 150-micron sieve.
Studies show calcitic limestones perform better than dolomitic due to higher solubility, and calcitic cations support better aggregation than magnesium-rich materials.
Effective $CaO$ content increases with finer particles (b150 μm) and decreases with coarser particles (N2.36 mm) and magnesium carbonate ( $MgCO_3$ ) content.

Lime Application Method and Tillage

Application methods depend on land use; lime can be top-dressed or incorporated by ploughing for arable crops.
Pelletized lime can be spread accurately using fertilizer-spreading equipment, requiring a reduced amount.
A single application is more effective than split doses and lime should be applied earlier and at a higher rate in no-tillage systems.

Soil Properties

Soil buffering capacity influences resistance to changes in ion concentration.
Soil pH is the simplest indicator for lime need; soil texture and organic matter content also influence lime requirement.
Sandy soils require less lime than soils with higher clay content, while higher organic matter levels also reduce lime needs.
Titratable acidity is primarily related to soil organic matter content.
Grassland liming recommendations suggest a positive response up to pH 6 (1 soil: 2.5 water) for mineral soils and pH 5.3 for peaty soils.
Cation exchange capacity, iron ( $Fe$ ) and aluminum ( $Al$ ) content also influence lime requirement, while soil moisture and temperature affect the reaction rate of lime.
The RothLime model predicts lime needs using soil pH and texture.

Impacts of Liming on Soil Processes

Neutralizing Acidity

Liming materials contain calcium ( $Ca^{2+}$ ) or magnesium ( $Mg^{2+}$ ) cations that displace hydrogen ions (H^+$) in the soil, neutralizing acidity.
For limestone, the reaction is: CaCO3 + 2H^+ \rightleftharpoons Ca^{2+} + CO2 + H_2O $</li> <li>For dolomite, the reaction is:$ CaMg(CO3)2 + 2H^+ \rightleftharpoons 2HCO3^- + Ca^{2+}Mg^{2+} $and$ 2HCO3^- + 2H^+ \rightleftharpoons 2CO2 + 2H2O $</li> <li>For calcium silicate, the reaction is:$ CaH2SiO4 + 2H^+ \rightleftharpoons Ca^{2+} + H4SiO4 $</li> <li>These reactions increase pH and can lead to an increase of the greenhouse gas$ CO_2 $.</li> <li>Neutralizing acidity impacts the biogeochemical cycling of carbon ($ C $), nitrogen ($ N $), and sulfur ($ S $).</li> </ul> <h4 id="soilbiotaandbiologicalprocesses">Soil Biota and Biological Processes</h4> <ul> <li>Liming impacts the abundance and composition of soil organisms like bacteria, fungi, archaea, nematodes, earthworms, and microarthropods.</li> <li>It increases the bacterial to fungal ratio, affecting decomposition rates and soil respiration.</li> <li>Changes in bacterial communities influence nitrogen cycling, while fungal community changes affect aggregate stability.</li> <li>Liming influences beneficial microbes like rhizobia and arbuscular mycorrhizal (AM) fungi, as well as pathogens.</li> <li>AM fungal root colonization tends to increase as soil reaches intermediate pH levels (5–6) and liming promotes AM fungal spore production.</li> <li>Improved conditions for rhizobia can benefit crop growth due to better nodulation and nitrogen fixation.</li> <li>Earthworms increase in abundance, leading to higher decomposition rates.</li> <li>Liming's impact on nematodes is complex, with evidence of increased abundance and changes in community composition.</li> <li>Liming-induced increases in soil pH have cascading effects on soil nitrogen transformation processes, influencing nitrogen supply to plants and nitrogen loss to the atmosphere or groundwater.</li> <li>Liming can increase soil microbial biomass nitrogen and activity, with stabilization at pH values between 5 and 7.</li> <li>Nitrogen mineralization can increase, but the overall impact depends on the carbon to nitrogen ratio of plant detritus.</li> <li>Liming impacts nitrate concentrations, affecting crop nutrient uptake and potentially increasing nitrate leaching risk, although some models suggest liming reduces nitrate leaching.</li> <li>Liming generally promotes nitrogen fixation, though the rate is influenced by microbial community composition.</li> <li>An extensive review shows that liming increases carbon dioxide flux and methane oxidation rates, while decreasing nitrous oxide emissions. However, overall greenhouse gas emissions may increase after liming.</li> <li>Agricultural liming is considered a net source of atmospheric$ CO_2 $, but long-term studies show that regular liming can increase soil carbon stocks or at least prevent net carbon losses.</li> <li>Liming increases biological activity, either by providing labile carbon forms to microbes or indirectly by increasing soil pH, which favors microbial groups that respire more carbon. Various mechanisms, such as increased root exudates and geochemical processes, may contribute to carbon sequestration in limed soils.</li> </ul> <h4 id="soilnutrientprocessesmineralsandheavymetals">Soil nutrient processes, minerals and heavy metals</h4> <ul> <li>Liming affects the availability of minerals and toxic elements, with effects on pH affecting biological and biochemical activity, mineralization, chemical adsorption, precipitation reactions, and plant nutrient uptake.</li> <li>Macronutrients include N, P, and K; micronutrients are trace elements needed by plants; heavy metals are also a concerm.</li> <li>Liming has a P-sparing effect, decreasing fixation of inorganic P by soil colloids and stimulates P uptake by plant roots</li> <li>The optimum pH for P for plants is in the rang of 5.5 and 6.5</li> <li>Liming can increase potassium adsorption and has effects on Sulphur.</li> <li>Increased levels of Ca are a the most direct effects, followed by Mg is dolomitic lime is used.</li> <li>Trace elements - liming reduces Zn, while increasing Cu and B.</li> <li>Heavy Metals - liming causes the adsorption of several heavy metals and reduces the risk of heavy metals being lost through leaching</li> </ul> <h4 id="soilphysicalcondition">Soil Physical Condition</h4> <ul> <li>Liming improves soil physical condition by changing pH and affecting soil chemical processes.</li> <li>Increasing ionic strength favors coagulation and micro-aggregate formation, increasing hydraulic conductivity and drainage.</li> <li>In sodic soils, liming improves soil structure, reduces dispersion, decreases penetrometer resistance, increases infiltration, and enhances water availability.</li> <li>Long-term liming improves aggregate stability and hydraulic conductivity, indicating improved soil function.</li> <li>Under field conditions, responses of soil physical conditions to liming are often not clear due to the diversity of minerals and organic matter, as well as the form, solubility, and timing of lime application.</li> <li>Calcium is involved in forming complexes at the micro-aggregate scale, stabilized to macro-aggregates by microbial activity.</li> <li>Liming-induced soil structural changes may be associated with increases in earthworm and enchytraeid populations, increasing total porosity and macroporosity.</li> <li>Time is a major factor in the formation of aggregates due to associations between calcium and organic matter.</li> </ul> <h3 id="impactsoflimingoncropsandgrassland">Impacts of Liming on Crops and Grassland</h3> <h4 id="yieldresponseofarablecrops">Yield Response of Arable Crops</h4> <ul> <li>Crop yields depend on the interception of photosynthetically active radiation (PAR), the efficiency of carbon fixation, and the allocation of carbon to harvestable tissues.</li> <li>Maximal growth requires adequate amounts of fourteen essential mineral elements and water.</li> <li>Liming affects water and mineral nutrient acquisition through chemical, physical, and biological effects on the soil.</li> <li>Soil pH influences the availability of chemical forms of mineral nutrients for plant uptake; liming increases the availability of most mineral nutrients except for manganese.</li> <li>Liming reduces problematic concentrations of$ Al^{3+} $and$ Mn^{2+} $in acid soils, which can increase the retention and availability of K+.</li> <li>Liming can alleviate calcium and magnesium deficiencies, especially with dolomitic lime ($ CaMg(CO3)2 $).</li> <li>Physical properties of the soil, influenced by liming, affect root foraging for mineral nutrients.</li> <li>While liming improves yields of most crops, the relationship between yield and soil pH differs between crops and is influenced by soil type.</li> <li>Field beans require pH N 6.0, wheat requires pH N 5.5, swede, kale and turnip require pH N 5.4, whereas potato can achieve maximal yields at pH 5.0</li> <li>Tolerance of acid soils is often related to an ability to prevent$ Al^{3+} $toxicity, often conferred by the release of organic acids at the root apex.</li> <li>Growth on acid soils can also be restricted by$ Mn^{2+}$$ toxicity or deficiencies of calcium, magnesium, phosphorus, or molybdenum.
In addition to yield effects, liming can improve nutritional quality by increasing concentrations of mineral elements required by livestock and humans, and reduce physiological disorders.

Crop Rotation of Arable Crops

A quarter of sugar beet and brassica vegetable crops have been limed in the British Survey of Fertiliser Practice, while 6% of winter wheat and field bean crops and 12% of spring barley and oilseed rape crops have been limed.
Soil pH of 5.5 was the optimal level for all crops across the whole rotation

Disease Implications for Arable Crops

Liming has important implications for the development of crop diseases, especially those which are soil-borne; acids soils tend to be more conducive to fungal infections and alkaline soils for bacterial and viral ones.
Some disease effects from liming are due to indirect effects on nutrient availability for plant metabolic processes, particularly those affecting defense mechanisms.
Pathogens such as Pythium ultimum produce more diseases at pH values less than 6 wherea Fusarium oxysporum produce more at > 6
Commom scab (potatoes) can be substantially reduced whene soil pH is < 5. 2 and it's because soil acidification provides effective control through the increase of streptmyces bacteria
Increased control for the diseade caused by a Pythium bacterial infection increases to control of cavity spot (carrots).
Severity of clubroot decreases on certain alkaline soil conditions, where the bacteria can no longer thrive

Biomass Production Response from Liming on Grassland

Positive for grazing and conserved Production and can only last for a short period (3-5 year)
Interactaction between Ca and P in perennial ryegrass with a p Sparing effect.
Liming responses are strongly related to the effect of lime on nutrient availablility.
Positive liming responses are directly proportional to the content of perennial ryegrass (competing more for Mineralization of soil organic N), since grassland composition varies depending on local environments

Liming Effects on Mineral Content and Herbage Quality in grassland

Application of lime changes the sward botanical composition, affecting the mineral contents in herbal quality and animal performance
Limining significantly increased the herbage content of both Ca and Mg
The use of dolomitic lime can also improve the Magnesium content of swards.
Liming has a significant impact on herbage quality, having a significant effect on animal performance (live weight gain and number of sheep grazing days)

Impacts of Liming Biodiversity

Vary context-specific, but soil pH is a major driver for plant community composition
Species richness general peas in neutral soils, and declines rapidly when pH drops below 5. In general, liming enhances the recovery of the species richness in soils.
Soil mesofauna respond to line additions differently (mites increased abundance soil).
Affect birds since earthworms are important food resources

Qualitative Framework

Outlines a distinctive and positive/negative impact from using different arable land management stratagies/biodiversity across the landscape
Uses a UK National Ecosystem assessment
Fig 5: Chronological scale, Properties/processes, and Function

Recommendations and Implications

Recommendations for Future Research

Need mechanistic and greater understanding

Process Level Focus

Molecular tools for improved detection and understanding for groups such as arthropods, Fungi and Archea. Also from different locations and varying soil conditions
Detail knowledge for all liming material influence how aggregate soil particular
Thorough investigation for how the effects of liming effect soil chem, in particularly in interaction withs P, K, and S

Ecosystem Level Focus

Estimating GHG and its emissions for selected soil types
There continues to be interest for how liming is beneficial to upland birds and estimating additional botanical/faunal changes develop